First report of Phytophthora citricola on Mangifera indica in Spain

T. Zea-Bonilla¹, P.M. Martín-Sánchez¹, J.M. Hermoso², M.P. Carmona³, E. Segundo³ and R.M. Pérez-Jimenéz^1*

¹ Instituto Andaluz de Investigación y Formación Agraria, Pesquera, Alimentaria y de la Producción Ecológica  (IFAPA-CICE). CIFA Churriana. Cortijo de la cruz s/n, Churriana, 29140, Málaga, Spain
2 Estación Experimental La Mayora (CSIC), 29750, Algarrobo-Costa, Málaga, Spain
³ IFAPA-CICE. CIFA La Mojonera, Autovía del Mediterraneo km 420, 04745 La Mojonera, Almería, Spain

^*patologia@olinet.es

Accepted for publication 31/08/06

In the last three years, mango trees (Mangifera indica) located in a fifteen-year-old orchard in the sub-tropical fruit-producing area of Andalucia (southern Spain) have developed symptoms such as wilting, chlorosis, sparse leaf production, microphylly and bark cracking (Fig. 1).  In July 2004, a Phytophthora species was isolated at low frequency from surface-disinfected necrotic roots using a Phytophthora-selective medium (Tsao & Ocana, 1969).

Figure 1: Symptoms on mango trees observed in the orchard from which Phytopthora citricola was isolated: wilting (left), chlorosis (centre) and bark cracking (right).

Figure 2: Colonies of Phytophthora citricola on PDA (A) and on V8A (B).
 

Colonies on potato dextrose agar had dense white aerial hyphae with a stellate pattern.  On V8 juice agar (V8A) they had sparse aerial hyphae with a radiate pattern (Fig. 2). Sporangia obtained in axenic cultures (Chen & Zentmyer, 1970) were semi-papillate, obovoid and 51 (28-52) x 36 (22-37) µm.  Paragynous antheridia, spherical oogonia and oospores of 28 (19-32) µm diameter, were homothallically produced on V8A (Fig. 3).  Ribosomal DNA (regions ITS1, 5.8S rDNA and ITS2) was amplified and sequenced (GenBank Accession No AM235209) and compared with sequences of known Phytophthora species obtained from GenBank.  The closest matches (99% identity) were with Phytophthora citricola.  Morphological and molecular results confirmed this species as Phytophthora citricola Sawada.

Figure 3: Semi-papillate sporangia of Phytopthora citricola in liquid medium (x 400) (left) and oogonium with paragynous antheridia formed on V8A (x 1000) (right).

A pathogenicity test was conducted using ten two-year-old mango plants (cv. Florida) growing in pots containing 15 L soil inoculated with sterile wheat seeds colonised by P. citricola (isolate CH455; Spanish Type Culture Collection, CECT 20567) from mango roots (25 g/L substrate).  Ten non-inoculated plants were used as controls.  No aerial symptoms were observed but 4 months after inoculation, P. citricola was recovered from necrotic roots of inoculated plants confirming its pathogenicity to mango.  In addition, detached mango leaves and stems of mango seedlings (cv. Gomera 3) were inoculated with mycelial plugs of isolate CH 455.  Lesions developed on leaves and seedlings and the pathogen was re-isolated (Fig. 4)

Figure 4: Mango stems inoculated with Phytophthora citricola (mycelial plugs): asymptomatic uninoculated control (left) and necrotic lesions on inoculated stems (right) after 10 days of incubation.

P. citricola causes root rot and trunk canker on many economically important plants, with reports of the disease on different hosts throughout Europe (Sawada, 1996).  To our knowledge, this is the first report of P. citricola occurring on mango trees and the first time this pathogen has been reported in Spain.  Our finding is important because the presence of P. citricola in this sub-tropical area represents a risk, not only to mango, but also to avocado (Persea americana), which is another susceptible host (Coffey et al., 1988).

References

Chen D, Zentmyer GA, 1970. Production of sporangia by Phytophthora cinnamomi in axenic culture. Mycologia 62, 397-402.

Coffey M, Oudemans P, Ouimette D, 1988. Phytophthora citricola: another cause of avocado decline. California. Avocado Society Yearbook 72, 127-31.

Sawada K, 1996. Phytophthora citricola. In: Erwin DC, Ribeiro OK, eds, Phytophthora Diseases Worldwide. St Paul, USA: APS Press, 282-287.

Tsao PH, Ocana G, 1969. Selective isolation of species of Phytophthora from natural soils in an improved antibiotic medium. Nature 223, 636-638.

The British Society for Plant Pathology